In fact, the effective radii for these \(N^*\)  production processes play an important role for this kind of spin selection.
With larger effective radius (\(r_{\text{eff}}\) ), the involved orbit angular momentum (\(L\) ) should also be larger because of \(L=r_{\text{eff}}\times p\) , where \(p\)  is the relative momentum of two hadrons in the final states or the initial states.
Since the size of \(N\)  is around 1 fm, the effective radius of the \(\pi N\)  and \(\gamma N\)  reaction will be around 1 fm.
For the \(N^*\)  with mass larger than 2 GeV, the momentum of \(N\)  is around 1 GeV at the rest frame of the \(N^*\) .
Thus the angular momentum of \(\pi N\)  will be \(L \sim r_{\text{eff}}\times p \sim 1 {\text{fm}}\cdot {\text{GeV}}\sim 5\) .
For the \(\pi N\)  and \(\gamma N\)  reactions, the total angular momentum (\(J\) ) of the initial state is from \(L-1/2\)  to \(L+1/2\)  and \(L-3/2\)  to \(L+3/2\) , respectively.
It leads to the spins of the \(N^*\)  resonances generated from \(\pi N\)  and \(\gamma N\)  being roughly from \(7/2\)  to \(13/2\) .
Correspondingly, the spins of \(N^*\)  resonances observed from \(\pi N\)  and \(\gamma N\)  reactions in Refs. [1]}, [2]}, [3]}, [4]}, [5]}, [6]} are all larger than \(5/2\) .
However, in the \(\psi \)  decay, the \(\bar{N}N^*\)  only can be generated from the annihilation of the charm and anti-charm quarks, therefore, the effective radius is small, hence leads to a small orbit angular momentum between \(\bar{N}N^*\) .
Thus, qualitatively speaking, the spin of \(N^*\)  generated from the \(\psi \)  decay cannot be very large. Indeed only \(N^*\)  with low spins were observed by BES collaboration in their PWA of various \(N^*\)  production processes from \(J/\psi \)  and \(\psi (2S)\)  decays [7]}, [8]}, [9]}, [10]}, [11]}.
